Composition of matter and method of making the same



' I UNITED STATES- Patented Sept; 8, 1 931 PATENT oFFIcE ELMER BL WELOH, OF MCKEESPORT, PENNSYLVANIA, ASSIGNOR TO FIRTH-STERLING STEEL COMPANY,.OF MCKEESPOR'I, PENNSYLVANIA, A CORPORATION 01, PENNSYL- VANIA oomosrnon or MATTER AND mn'rnon or MAKING THE SAME No Draw ing This invention relates generally to compositions of matter useful for making tools 'such'as drawing dies, extrusion dies; hi h speed'cutting tools such as bits, shapers, dril s,

5 cutters, saws and the like; dressing tools such as grinding stones, knife Sharpeners andthe like.

It has been known heretofore to make tools by mixing finely divided tungsten carbide with finely divided cobalt, and to thereafter subject the mixture to heat suflicient to sinter it and pressure sufficient to form the article into the desired shape. I v

It is desirable in some instances to use in is place of the cobalt as binding agent, an alloy composed of twoor more metals, such, for example, as cobalt, copper, iron, chromium, ornickel. The natural way to form such an alloy binding agent, for example, a binding agent alloy composed of cobalt and copper,

would be to grind with the cutting agent, such 'aspow'dered tungsten carbide, both powdered cobalt and powdered copper. It has been found, however, that there is some dlfliculty in obtaining an intimate'mixture of the tungsten carbide, cobalt and copper, when all of. thesematerials are used in powdered form.

and are ground together to form the composition which is to be subjected to the sinter- 1 a0 ing operation. This is particularly true in cases where a large percentage of tungsten-- carbide is mixed with small percentages of powdered cobalt and powdered copper. Even though the grinding is carried out for and copper to segregate so as to produce an unhomogeneous mixture. The ditficulty 1n obtaining an intimate mixture of powdered tungsten carbide. powdered cobalt, and powdered copper is further increased due to the fact that the tungsten carbide powder is much heavier than either of the other elements. If an intimate mixture of tungsten carbide,. co bait, and copper is not pro need, the article resulting from the sinteriqg of the mixture is not homogeneous and is not as efiicient in performing its function as it should be.

I have found that an intimate mixture of the cobalt and copper can be obtained by coating the cobalt with copper. This insures that a long time, there is a tendency for the cobalt Application filed September 27,1929. Serial No. 895,748.

in the subsequent sintering operation the cohalt and copper will alloy to form the alloy b1nd1ng agent, whereas, if both the cobalt and copper were used in powdered form, these elements would tend to segregate so that there would not be intimate contact between them. If there is not an intimate contact between the cobalt and the copper, there is difiicultyin forming an alloy of these elements in the sinterin operation. The method of forming an a loy binding agent by coating one of the metals which goes to make up the alloy with one or more metals which it is desired to alloy with the first metal, insures that in the subsequent sintering operation the desired binding metal alloy will be formed. The method of coating a binding metal with another metal which will alloy therewith in the subsequent sintering operationeliminates any tendency to segregation which might take place if the metals which it is desired to alloy to form the alloy binding agent wereeach used in powdered form. I

In accordance with my invention, a bind-' is first coated with a metal and the coated particles of binding agent are'then mixed Wlth finely divided particles of a cutting agent or cutting agents suchas tungsten car adhere together and take the desired form of article; 4 As a specific example of the manner of practicingmy inventlon, a binding agent such as cobalt is pulverized to a very finely divided condition, preferably to a fineness such that it will pass through a 200 mesh screen. The cobalt in finel divided form is then coated with a layer ,0 copper either by immersing the cobalt 'in a solution containing copper or by electro-deposition from a copper solution. A satisfactory method is to'dip the cobalt particles in a solution of copper sulphate. The cobalt particles are coated to such an extent that the copper'coating constitutes by weight from .2 per cent to 20 per cent of the co alt particles. 1

In usual practice the copper coating constitutes from 2 to per cent by weight of the cobalt particles. Very good results have been obtained by coating the cobalt particles with copper in an amount such that the copper constitutes by weight about 3% per cent of the cobalt .particles. The coated cobalt particles are then mixed with a cutting agent or a mixture of cutting agents such as tungsten carbide,'vitrified zirconium oxide or silicon carbide. The mixture of cutting agent in finely divided form and cobalt particles also in finely divided form but coated with copper, are then subjected to heat and pressure in order to cause the coated particles of cobalt to fuse and bond together the particles of cutting agent.

In the above example I have used tungsten carbide as the cutting agent and cobalt as the binding agent, the binding agent being coated with copper. The invention, however,- is not limited to theseparticular elements but on the contrary any suitable cutting agen't such, for example, as vitrified zirconium oxide or silicon carbide can be used. In place oi cobalt as a binding agent I may use iron or an alloy steel such, for example. as high speed steel. Furthermore, the binding agent instead of being coated with copper may be coated with chromium or nickel. or first with one of these metals and then with another.

I have found that if the particles of binding agent are first coated with copper and then coatedwith chromium, and the method as above described is carried out, it results in an article which is extremely tough and which will withstand usage for very long periods of time. When the particles of binding agent are coated with both copper and chromium, the copper should constitute by weight from .1 per cent to per cent of the binding agent. The copper preferably constitutes from 1 per cent to 2 per cent of the weight of the binding agent. The chromium should'constitute by weight from .1 per cent to 10 per cent of the binding agent and preferably from lper cent to 3- per cent. It has been found that very good results are obtained whenthe copper constitutes about 1 per cent, and the chromium about 2 per cent by weight of the binding agent. 7

As above stated, the particles of binding agent, after having been coated with metal, are mixed with finely divided particles of cuttingagent and the mixture is subjected to heat and pressure. The proportion of cutting agent and binding agent varies according to the type of article which it is desired to produce. I

Where brittleness of the product is not a limiting factor, small percentages of binder may be used, but where strength and resistance to shock are required, larger percent ages of binder must be present. It is notable that where the binder is increased, the cutting while in cases where great strength and toughness is required in the composition, the binding agent may be increased up to 95 per cent. In the production of cutting tools, the cutting agent should constitute at least per cent of the composition. Usually the cutting agent constitutes about per cent and the binding agent about 10 per cent.

The mixture is heated to a temperature of "about 280Q F. in order to fuse the coated particles of binding agent and to cause them to firmly bond the particles of cutting agent.

The pressure for shaping the article may be exerted on the mixture either before the heating step or during the heatin step or after the heating step has been finis ed. Suitable precaution should be taken during the heating in order to prevent oxidation. This may be accomplished byheating in a neutral or reducing atmosphere.

Throughout the foregoing description where I have referred to tungsten carbide,

I preferably utilize a carbide having approximately 6 per cent of carbon combmed with the tungsten. v

n the specification and claims I have used metal in its broad senseto include not only a single metal but a mixture or alloy of several metals. I

Tools produced in accordance with my invention have'been' found to be materially.

tougher than those roduced by mixing a.cut-

ting agent or cutting agents with a binding agent or agents, both in powdered form, and then heating and pressing the mixture. The exact theory or underlying principle which results in the improved characteristics of compositions made in accordance with my invention is not definitely known. It is thought, however, that where the particles of binding agent are coated with a layer of metal such as copper or copper and chromium, this coating forms a tough bonding medium in which the particles of cutting agent are firmly embedded.

" I have described the present preferred embodiment of my invention, but it should be understood that it may be otherwise embodied or practiced within the scope of the following claims:

I claim:

, 1. The method of making a composition of matter comprising coating finely divided particles of cobalt with copper and then with chromium, mixing the coated particles with finely divided tungsten carbide, and subjecting the mixture to heat and pressure.

2. The method of making a composition of matter comprising electroplating finely divided particles of cobalt with copper and then coating the previously coated particles with chromium, mixing the coated particles with finely divided tungsten carbide, and subjecting the mixture to heat and pressure. 3. The method of making a composition of matter, comprising coating finely divided particles of metal of the group containing cobalt, iron, nickel, copper and chromium with another metal of said group, mixing the coated particles with abrasive particles of the group containing tungsten carbide, silicon carbide, and vitrified zirconium oxide, and sintering the mixture.

4. The method of making a composition of matter, comprising coating finely divided particles of cobalt with copper, mixing the coated particles with abrasive particles of the group containing tungsten carbide, silicon carbide, and vitrified zirconium oxide, and sintering the mixture.

5. The method of making a composition of matter, comprising coating finely divided particles of cobalt with copper, mixing the coated particles with tungsten carbide, and sintering the mixture.

6. The method of making a composition of matter comprising electroplating finely divided particles of cobalt with a metal of the group containing copper, nickel and chromium, mixing the coated particles with finely divided particles of tungsten carbide, and sintering the mixture.

7. The method of making a composition of matter comprising electroplating finely divided particles of cobalt with copper, mixing the coated particles with finely divided particles of tungsten carbide. and sintering the mixture.

8. A composition of matter comprising tungsten carbide particles bonded by an alloy of cobalt and copper, the copper constituting from 0.2 to by weight of the cobalt, the tungsten carbide constituting at least 80% by weight of the composition.

9. -A composition of matter comprising tungsten carbide particles bonded by an alloy of cobalt and copper, the copper constituting from 2 to 5% by weight of the cobalt, the tungsten carbide constituting at least 80% by weight ofthe composition.

10. A composition of matter comprising tungsten carbide particles bonded by an alloy of cobalt with a small proportion of 55 copper and chromium, the tungsten carbide constituting at least 80% by weight of the composition.

In testimony whereof I have hereunto set my hand. ELMER B. WELCH. 

